Side dumping vehicles customarily employ gate panel operators to control opening and closing of the side panel or sideboard along one side of the dump box. Typically, the side panel is pivotally secured along its lower margin to the box and is adapted to swing outwardly and downwardly about its pivotal or hinged connection to the box as the dump box is tilted or otherwise lifted into the dumping position so as to permit the contents of the box to be expelled by gravity. Ordinarily, in the past, gate panel control mechanisms have required manual assistance or some positive means of control running from the gate panel control to the cab of the vehicle. Representative of such approaches are disclosed in U.S. Pat. Nos. to Triggs 3,493,265 and Maxey 4,087,129. In the latter, a cable is extended between the gate and a motive drive system and requires positive operation of that drive system in order to operate the gate panel between the opening and closing positions.
Other systems have been devised which are designed to operate automatically in response to lifting and lowering of the dump box to regulate opening and closing movement of the gate panel. Generally, however, such systems have required fairly sophisticated mechanisms and adjustments to conform to each size and type of dump box and are either expensive or difficult to manufacture and install. Most importantly, however, such operators have not been designed in such a way as to cause premature opening of the gate panel so as to avoid imposition of substantial loads on the gate panel as the dump box is tilted into the unloading position. In other words, the weight of the load in the dump box is at least partially relied upon to impart opening movement to the gate panel. Representative of gate panel operators which operate in response to tilting movement of the dump box are U.S. Pat. Nos. to Ballou 1,300,810, Fraunfelder 2,595,836, Orendorff 2,437,890 and Correa 2,394,153. Also representative of such gate panel operators are Canadian Pat. No. 1,000,763 and German Pat. No. 24,215. For instance in Orendorff, a side linkage mechanism is regulated by a motive drive system in the form of a hydraulic unit to control opening and closing of a dump cart. In Fraunfelder, a compression column operates in association with a rocker member and actuator link as somewhat of a toggle mechanism in controlling the opening and closing movement of a gate panel. Similarly, the patent to Correa discloses a toggle-type mechanism to control opening and closing of a side board for a dump box with a spring-loaded return mechanism to cause the side board to return to its original closed position after the unloading operation.